An industrial robot comprises a manipulator and control equipment. The manipulator comprises at least one robot arm comprising a number of arm parts with connecting joints, where the axes of rotation of the joints define the degrees of freedom of the robot. As an example may be mentioned a six-axis robot which usually has a fixed foot, a stand that is arranged on the foot and that is rotatable about a first axis, and a first robot arm that is rotatable in relation to the stand about a second axis. At the outer end of the first robot arm, a second robot arm is rotatably journalled for rotation about a third axis. This second arm is rotatable about a fourth axis, its own longitudinal axis, and at its outer end supports a robot hand provided with a tool attachment, said robot hand being rotatable in two degrees of freedom about a fifth and a sixth axis, respectively, relative to the second arm.
The movements of the manipulator are made possible by the arrangement of drive means that bring about rotary motions in the respective joints. Each drive means comprises an electric motor and a reduction gear. The power supply and the control of an industrial robot of the kind mentioned above are carried out by control equipment, which is not described in more detail in this context.
The working range and the capacity for movement of a manipulator depend, among other things, on the reduction gears included. An additional factor that is influenced by the reduction gears is the performance of a robot with respect to precision and/or accuracy. When manufacturing industrial robots, the aim is to arrive at design solutions which enable reducing the total built-in backlash from the gears included therein as much as possible.
According to prior art (FIG. 12) in the form of a wrist for an industrial robot, spacers, also called shims, are used to eliminate the backlash from the gears. The method comprises the steps of calculating in advance how large the backlash will be, building together the manipulator/the wrist and then measuring the actual remaining backlash. When the calculation does not correspond to the physical result, the manipulator/wrist must be detached and the process started over again with a new, hopefully more correct calculation. This is a time-consuming and expensive process.
For the above reasons, there is a need of a simple and rapid method to be able to adjust the backlash when mounting gears in a manipulator. This need cannot be satisfied by the prior art.